1. Field of the Invention
The present invention relates to a map data processing unit capable of updating map data without affecting the operation speed of its navigation function with minimizing the time of precluding the use of the navigation function.
2. Description of Related Art
A conventional vehicle-mounted navigation system or the like usually operates on map data stored in a recording medium such as a CD-ROM or DVD-ROM, and updates the map data by changing the CD-ROM or DVD-ROM. The method, however, cannot update the data frequently, only once or twice a year at most, and hence it cannot always provide the latest map data.
In contrast with this, a method is proposed of updating the map data in a shorter period of time by storing the map data in a rewritable medium (refer to Relevant Reference 1, for example).
Relevant Reference 1: Japanese patent application laid-open No. 2002-49624 (page 4, FIG. 7).
With such an arrangement, the conventional map data processing unit updates the map data when it becomes necessary. Thus, when using a plurality of map data in processing such as route search, it imposes a heavy load on the navigation system, thereby presenting a problem of retarding the operation.
In addition, carrying out the update processing of all the map data at once offers a problem of precluding the use of the vehicle-mounted navigation because the update processing takes a lot of time. For example, to rewrite all the map data by reading data from a DVD-ROM, about nine gigabit data must be read. Since a current DVD-ROM drive usually reads about 1–2 MB per second, it takes about 1–2 hours to read the map data, with precluding the use of the navigation during that time.